This invention relates to a propeller for use in ships.
Usually the maximum diameter of a propeller for use in ships is designed to produce a maximum propelling efficiency at its designed operating point. However, it is generally obliged to make smaller the diameter than the optimum diameter due to the relation between the propeller and the draught line as well as the limitation imposed by vibrations. For this reason, the propellers are used at a considerably inefficient state from the viewpoint of their best efficiencies. To improve the propelling efficiency, it has been proposed the so-called tandem type propeller in which two propellers are coaxially mounted on the same propeller shaft. This design, however, not only lengthens the propeller shaft but also requires reinforcing the bearing that supports the propeller shaft. Moreover, due to the spacing between the tail of the ship and a rudder plate it is difficult to substitute the tandem type propeller for an existing propeller.